This invention relates to a bar feed mechanism actuated by hydraulic fluid for advancing elongated bar stock into the spindle of a machine tool such as an automatic or semi-automatic lathe, screw machine and the like.
Feed devices for bar stock are well known which utilize mechanical and/or pneumatic means for feeding bar stock. These have the disadvantages of noisy operation and tendency to damage the bar stock when rotated by the spindle of the machine tool. Hydraulic bar feed devices have also been developed which avoid the above disadvantages, but to the best of applicant's knowledge none of the prior art hydraulic bar feed devices has been completely successful due to one or more of the drawbacks of relatively complex and hence expensive structure; in some instances inability to retract the feeding device hydraulically after a length of stock is used up; failure to prevent oscillation of the bar stock during feeding, particularly when the bar stock is rotated rapidly; difficult and time-consuming arrangements for reloading with a fresh length of bar stock; and inability to accommodate a wide range of diameters (or cross-sectional shapes) of bar stock.
It is a principal object of this invention to provide a bar feed mechanism which avoids the above-noted disadvantages of prior art mechanical, pneumatic and hydraulic bar stock feeding apparatus.
To this end there is provided, in accordance with the present invention, a bar feed mechanism comprising a cylindrical tube, a piston movable axially within the tube, a shaft rotatably secured to the piston and projecting therefrom toward the machine tool, a cylindrical centering sleeve rotatably mounted on the shaft and axially movable thereon, center means secured to the shaft at the end thereof remote from the piston, the center means having a concave surface for engaging the trailing end of a bar, a bushing at the end of the tube adjacent the machine tool having an orifice which permits passage of the centering means therethrough but retains the centering sleeve, an hydraulic pressure inlet for admitting fluid behind the piston to cause movement thereof in a feeding direction, means to admit pressure fluid between the piston and the centering sleeve, and pressure relief means to permit drainage of hydraulic fluid from the tube between the piston and centering sleeve when the sleeve abuts the bushing. Preferably a reversible pump is provided to withdraw hydraulic fluid from the tube under subatmospheric pressure, thereby effecting retraction of the piston, shaft, sleeve and center means after completion of a feeding stroke.
U.S. Pat. No. Re. 29,905 discloses a cylindrical tube, a piston in the tube, a stock pusher comprising a rod with a pushing head having a conical recess which engages a piece of bar stock. Hydraulic fluid under pressure acts on the piston to push the bar stock toward a machine tool. The piston is provided with an inner channel having an adjustable cross-section and regulating means in the inner channel for adjusting the cross section, so that oil supplied under pressure passes the piston with loss of pressure in an amount determined by the regulating means. The piston is provided with clearance around the outside thereof relative to the tube, and the pushing head has greater clearance in the tube than the piston. There is also provided a ball-check valve allowing oil to flow from behind the piston to the front of it when it is desired to return the bar pushing mechanism for reloading.
U.S. Pat. No. 4,217,800 discloses a bar feed device comprising a guide tube which may be a pneumatic or hydraulic cylinder having at the rear end thereof a closed tube of smaller diameter. A first piston is slidable in the larger diameter guide tube and is provided with a holder having a stepped opening for insertion of a rod. The holder is rotatable with respect to the primary piston body. A second piston is provided having a telescoping engagement with the first piston, and the second piston is provided with an ejection rod which projects forwardly through the holder. An embodiment adapted for thin rod materials includes an additional piston in front of the first piston and a buckle guide tube, in order to prevent buckling of thin rods during feeding. Reloading of a new bar is effected manually after exhausting pressure behind the first piston.
U.S. Pat. No. 4,034,632 discloses a bar feed device comprising a feed tube having a feed piston therein with two telescoping parts. The smaller diameter part or piston has on its front end a centering head which is rotatable and provided with a conical bore to receive the end of a bar to be fed. The larger part or piston is first caused to move toward the machine tool by fluid pressure until it abuts against a stop, after which hydraulic fluid passing through apertures therein acts on the rear of the smaller part or piston and forces it farther in the feeding direction. The smaller piston and centering head have an outside diameter which permits them to enter the spindle hole of the machine tool. A back rest in the form of rollers and associated cams actuated by pneumatic means is provided to prevent oscillation of the bar stock.
U.S. Pat. No. 3,074,566 discloses a bar feed having an outer tube and a concentric inner tube forming a cylinder within which a piston reciprocates. At the forward end of the inner tube a two-piece bushing is provided which is removably held in place, and bushings of different size apertures may be provided for bar stock of different diameters. The piston is provided with a flexible cup or gasket to vary the clearance at the rearward end thereof. A plurality of bearings is arranged within the inner tube in front of the piston which are rotatable and slidable within the tube. A separate socket having a conical recess at the outer end thereof is provided in front of the bearings, and the socket and bearings may rotate with the bar stock without transmitting rotation back to the piston. It is contemplated that the socket and some of the bearing members may enter the spindle of a lathe in order to feed all of the bar into the lathe. This in turn forces the bushing out of the end of the inner tube. Pressure fluid is admitted into the outer tube and passes from the outer tube into the rear of the inner tube through an opening provided therein.
U.S. Pat. No. 2,701,355 discloses a hydraulically operated bar feed device having a tube, a reciprocating piston, the piston being of two-piece construction, at the front end of which is a reduced shank having a recessed depression to engage the end of a bar. The forward end of the tube is crimped inwardly to form a stop through which the shank passes but which retains a shoulder of the enlarged body portion of the piston. At the other end of the piston a washer is provided with means for adjusting the seal fit of the washer. Such an arrangement can feed only a single size of bar stock.
U.S. Pat. No. 2,572,741 discloses a bar feed device comprising a tube, a plunger, a shaft extending forwardly of the plunger, a stem extending rearwardly from the plunger, and a traveler having a conical recess at the end thereof to engage a piece of bar stock. The plunger includes sections through which the stem extends and on which they are slidable. The shaft is of relatively small diameter and is connected to the traveler in such manner that it may both slide and turn therein. The forward end of the traveler is reduced in diameter to form a pilot portion which can project beyond the discharge end of the feed tube, but the rear portion of the traveler is of a diameter which is retained when it abuts the discharge end. This arrangement is actuated by compressed air and apparently is reloaded with a fresh bar manually after air pressure is vented from the rear end of the tube.
Other prior art relating to bar feed mechanism include U.S. Pat. Nos. 2,300,457; 2,334,272; 2,548,786; 3,162,315 and British Patent No. 1,201,904.
A preferred bar feed mechanism for a machine tool, in accordance with the invention, comprises at least one elongated cylindrical tube of uniform inside diameter, closure means at the end of the tube remote from the machine tool, a piston movable axially within the tube, a pusher shaft rotatably secured to the piston and projecting therefrom toward the machine tool, a cylindrical centering sleeve rotatably mounted on the shaft and axially movable thereon within the tube, the piston and the centering sleeve each having a close sliding fit within the tube, center means releasably secured to the shaft at the end thereof remote from the piston, the center means having a concave surface at its end remote from the piston for engaging a trailing end of a bar being fed to the machine tool, the centering sleeve being interposed on the shaft between the piston and the center means, a bushing at the end of the tube adjacent the machine tool having an axial orifice therein of a diameter sufficient to permit passage of the center means therethrough but to retain the sleeve, a source of hydraulic fluid under pressure, an inlet for the pressure fluid in the closure means at the end of the tube remote from the machine tool for moving the piston and the shaft toward the machine tool in a feeding direction, at least one additional inlet intermediate the ends of the tube for admitting pressure fluid ahead of the center means, means to admit pressure fluid between the piston and the centering sleeve, and pressure relief means in the tube effective after movement of the sleeve therebeyond in the feeding direction to drain pressure fluid from the tube between the sleeve and piston whereby to permit continued movement of the piston, shaft and center means in the feeding direction.